F-35 - A paradox?
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F-35 - A paradox?
My wife has just bought me a glossy magazine which features the F-35 Lightning.
All very interesting.
Now, throughout my life I was always led to believe that for supersonic flight swept wings were best (EE Lightning).
In terms of 'stealth' geometric shape was best (F-117).
In the form of the F-35 we have a straight-winged aeroplane with stubby wings and curves, looking like it's been put together from an Airfix kit with the parts of several models in the wrong place.
How, why?
John Farley and Co - please explain?
Kind regards
FOK
All very interesting.
Now, throughout my life I was always led to believe that for supersonic flight swept wings were best (EE Lightning).
In terms of 'stealth' geometric shape was best (F-117).
In the form of the F-35 we have a straight-winged aeroplane with stubby wings and curves, looking like it's been put together from an Airfix kit with the parts of several models in the wrong place.
How, why?
John Farley and Co - please explain?
Kind regards
FOK
Do a Hover - it avoids G
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F/O Kite
In the old days due to various structural factors people could not make wings with less than a thickness chord ratio of about 8 or 10% (or even more) without them being too 'floppy'.
If you take one such 'thick' wing and bend it back (like the Lightning you mention) then the oncoming AIR sees effectively a much increased chord for the same thickness/spar depth - hence the spar is more streamlined and offers less drag.
Straight wings (if you can make them thin enough) avoid a lot of the stability and control as well as handling problems that are inevitably going to arise with sweepback.
If you take one such 'thick' wing and bend it back (like the Lightning you mention) then the oncoming AIR sees effectively a much increased chord for the same thickness/spar depth - hence the spar is more streamlined and offers less drag.
Straight wings (if you can make them thin enough) avoid a lot of the stability and control as well as handling problems that are inevitably going to arise with sweepback.
Stealth
As I understand it:- In the F-117 (developed decades ago) the stealth features were designed using the best mathematical tools and models of the day. Constrained effectively by the limitations of the computers of the time. This resulted in the weird angular shapes.
Today, computers are thousands of times, or maybe much more, faster. Perhaps in conjunction with better theory, this has allowed more flexibility in the choice in the profiles of the aeroplane while still being able to meet the required stealthiness.
Putting on Victor Meldrew hat - I CAN'T BELIEVE IT!!!
The pprune spell checker doesn't like "aeroplane". Or as it now turns out "pprune" either:-)
The short answer is - computers have changed everything, get with the program or go and live with the bears:-)
Today, computers are thousands of times, or maybe much more, faster. Perhaps in conjunction with better theory, this has allowed more flexibility in the choice in the profiles of the aeroplane while still being able to meet the required stealthiness.
Putting on Victor Meldrew hat - I CAN'T BELIEVE IT!!!
The pprune spell checker doesn't like "aeroplane". Or as it now turns out "pprune" either:-)
The short answer is - computers have changed everything, get with the program or go and live with the bears:-)
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Here's the term for what all three prior posts are describing...
"design space"
Design space is a term that has been used by R-and-D teams for some years. It is an imaginary, immeasurably vast volume in which all possible designs exist-all possible designs whether extinct, extant, as yet unrealized, or never to be realized. (This definition is a direct quote from "On the Origin of Teepees" by author Jonnie Hughes of Torquay, Devon)
As technology advances in one venue it will allow developers in other specialties to reach higher into their own design space.
The short answer is -
Design space is a term that has been used by R-and-D teams for some years. It is an imaginary, immeasurably vast volume in which all possible designs exist-all possible designs whether extinct, extant, as yet unrealized, or never to be realized. (This definition is a direct quote from "On the Origin of Teepees" by author Jonnie Hughes of Torquay, Devon)
As technology advances in one venue it will allow developers in other specialties to reach higher into their own design space.
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F-35 wings are most definitely swept and stealth shaping has moved on a very long way since the F-117.
Take a look at the F 104 wing; it has a very similar planform and only precedes the F35 by about 50 years.
As for curves I recall reading somewhere that HS Hawks had a remarkably low RCS from certain angles, this was attributed to the shape of the fuselage, but jimjim is right, the computer has made it possible to design and test much more readily. The B-2 is an excellent example of this and precedes the F-35 by about 10 years
VIDEO: F-35B completes first shipboard vertical landing
There is a video on the FlightGlobal website showing a VTOL landing by an F-35B.
VIDEO: F-35B completes first shipboard vertical landing - The DEW Line
Interestingly, the lateral transition across the edge of the deck has been edited out. Could that be due to an embarrassing wobble over the edge?
VIDEO: F-35B completes first shipboard vertical landing - The DEW Line
Interestingly, the lateral transition across the edge of the deck has been edited out. Could that be due to an embarrassing wobble over the edge?
Not really, it was designed that way for other reasons and radar stealth wasn't really on the agenda at that time.
On the other hand - the Mosquito a few years earlier was very much a stealth aircraft and the radar near-invisibility of the wooden airframe was used to good effect. Again however, that was probably luck rather than something at the design stage.
G
On the other hand - the Mosquito a few years earlier was very much a stealth aircraft and the radar near-invisibility of the wooden airframe was used to good effect. Again however, that was probably luck rather than something at the design stage.
G
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JSF always sounded like a Paradox
Please indulge two layman's questions:
1) This more stable design of the F-35 presumably makes it a good strike aircraft or are targeting devices so good these days that it's irrelevant (I imagine not, but..)?
2) Depending on the answer to the above, making Typhoon an all-rounder must take a lot of expertise and making the F-35 a 'fighter' a similar challenge?
Have seen the fuselage for the F-35 being manufactured - astonishing accuracy and engineering, so I have nothing but respect for those involved.
1) This more stable design of the F-35 presumably makes it a good strike aircraft or are targeting devices so good these days that it's irrelevant (I imagine not, but..)?
2) Depending on the answer to the above, making Typhoon an all-rounder must take a lot of expertise and making the F-35 a 'fighter' a similar challenge?
Have seen the fuselage for the F-35 being manufactured - astonishing accuracy and engineering, so I have nothing but respect for those involved.
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I guess it's the integration of the whole. These modern ac are referred to as weapons systems for a reason; there is a limit to how accurately a dumb weapon can be delivered,smart weapons can be much more accurate if there is some terminal guidance pointing it at the right spot.
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OK Kitbag I'll bite. The official designation of the wing shape for the F35 is the so called large area clipped delta. Very similar in shape and design to the F22 wing, but on a smaller scale. I agree that it is not a purists swept wing, but for the layman the leading edge surely satisfies the criteria of a 'swept' wing. To compare it to the F104 wing is, in my opinion folly. Two very different design drivers at work.
Any and all aircraft will have a small RCS from 'certain angles' the key is knowing where those angles are.
Any and all aircraft will have a small RCS from 'certain angles' the key is knowing where those angles are.
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Must depend on what angle, surely
Likely get bitten here, but the angles are going to be changing all the time, so 'certain angles' must be a moveable feast.
My impression was that there is a lot more to a low RCS than that. Takes me back to the manufacturing side, but enough is enough, I think.
Kitbag - thanks for your reply.
My impression was that there is a lot more to a low RCS than that. Takes me back to the manufacturing side, but enough is enough, I think.
Kitbag - thanks for your reply.
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Now, throughout my life I was always led to believe that for supersonic flight swept wings were best (EE Lightning).
Sorry, the English E. Lightning's planform is not the ultimate macroscopic design for a supersonic fighter plan. I ain't disrespectin' the Lightning -- it was a good design for its time.
For supersonic flight, it's important to keep the wings and tail as much as possible inside the Mach cone(s) the aircraft's bow shock wave creates.
Google "Mach cones."
Sweeping the wings back `a la mode EE Lightning back is one way, but not the only way, to keep the wings and horizontal stabilizer inside inside the Mach cone.
However, a long-ish wingspan swept back 50 or 60 degrees also has drawbacks. Got to Swept wing - Wikipedia, the free encyclopedia and scroll down to the "Disadvantages" section.
Sorry, the English E. Lightning's planform is not the ultimate macroscopic design for a supersonic fighter plan. I ain't disrespectin' the Lightning -- it was a good design for its time.
For supersonic flight, it's important to keep the wings and tail as much as possible inside the Mach cone(s) the aircraft's bow shock wave creates.
Google "Mach cones."
Sweeping the wings back `a la mode EE Lightning back is one way, but not the only way, to keep the wings and horizontal stabilizer inside inside the Mach cone.
However, a long-ish wingspan swept back 50 or 60 degrees also has drawbacks. Got to Swept wing - Wikipedia, the free encyclopedia and scroll down to the "Disadvantages" section.
Couple of points:
JF is right, of course. I think the last design I saw with a classic highly swept wing was Dassault's ACF (Avion de Combat F**tu, as disrespectful people called it) which was whacked in 1975 in favor of the M2000.
The F-104 indeed had an unswept wing. It's interesting to look at some recent research into supersonic laminar flow (eg Aerion SSBJ) and wonder why the '104 was so notoriously slippery.
Today, we have a few fighter design groups. There are lots of low-sweep (at the quarter chord) wings, evolutionary descendants of the F-5. Canard deltas roam unchecked from Linkoping to Chengdu. The T-50 PAK-FA looks like the F-22's delta wing interbred with MiG-29/Sukhoi "centroplane" which in fact looks a lot like NASA's arrow wing.
LOAgent - That's kind of an odd name for the wing. On the A and B it has been clipped to the point where it no longer looks like a delta at all. The C, not so much, and from some angles it is vaguely reminiscent of a Javelin.
Where the A and B, certainly, are unique is the size of the wings proper, relative to the total span and gross area. Unless there is some aerodynamic subtlety for making the body produce lift efficiently and at low alpha (like the Russian centroplane) the lift distribution plot will have a big dip in the middle and the outer wings will be working hard.
That may be the case: Consider that the C's outer wings are almost twice the size of the A/B's to get down to a 140-some-kt carrier approach speed.
Also, there is a very tight (=high rotational velocity) vortex off the wingtips visible in many photos, and the only maneuver I have seen in videos is a lazy roll that resembles a fat lady being pitched out of an upper berth as an unexpected swell catches the Harwich-to-Hook of Holland ferry...
JF is right, of course. I think the last design I saw with a classic highly swept wing was Dassault's ACF (Avion de Combat F**tu, as disrespectful people called it) which was whacked in 1975 in favor of the M2000.
The F-104 indeed had an unswept wing. It's interesting to look at some recent research into supersonic laminar flow (eg Aerion SSBJ) and wonder why the '104 was so notoriously slippery.
Today, we have a few fighter design groups. There are lots of low-sweep (at the quarter chord) wings, evolutionary descendants of the F-5. Canard deltas roam unchecked from Linkoping to Chengdu. The T-50 PAK-FA looks like the F-22's delta wing interbred with MiG-29/Sukhoi "centroplane" which in fact looks a lot like NASA's arrow wing.
LOAgent - That's kind of an odd name for the wing. On the A and B it has been clipped to the point where it no longer looks like a delta at all. The C, not so much, and from some angles it is vaguely reminiscent of a Javelin.
Where the A and B, certainly, are unique is the size of the wings proper, relative to the total span and gross area. Unless there is some aerodynamic subtlety for making the body produce lift efficiently and at low alpha (like the Russian centroplane) the lift distribution plot will have a big dip in the middle and the outer wings will be working hard.
That may be the case: Consider that the C's outer wings are almost twice the size of the A/B's to get down to a 140-some-kt carrier approach speed.
Also, there is a very tight (=high rotational velocity) vortex off the wingtips visible in many photos, and the only maneuver I have seen in videos is a lazy roll that resembles a fat lady being pitched out of an upper berth as an unexpected swell catches the Harwich-to-Hook of Holland ferry...
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1) This more stable design of the F-35 presumably makes it a good strike aircraft or are targeting devices so good these days that it's irrelevant (I imagine not, but..)?
Define stability. Why do you say the F-35 is more stable?
2) Depending on the answer to the above, making Typhoon an all-rounder must take a lot of expertise and making the F-35 a 'fighter' a similar challenge?
Why is the F-35 deficient as a fighter? Please tell us.
... Are you merely repeating things you've heard at nth hand on some other aircraft chat board? That's not a good habit.
Define stability. Why do you say the F-35 is more stable?
2) Depending on the answer to the above, making Typhoon an all-rounder must take a lot of expertise and making the F-35 a 'fighter' a similar challenge?
Why is the F-35 deficient as a fighter? Please tell us.
... Are you merely repeating things you've heard at nth hand on some other aircraft chat board? That's not a good habit.
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Without repeating the expert commentary available at Air Power Australia, can a mug pilot tell if the JSF (F-35) is really a fighter of practical use for airspace domination?
I think so.
The airframe is small. Small airframes are associated with limited fuel capacity and thus range. A small airframe won't carry a lot of bulky, heavy weaponry plus heaps of internal fuel to fly fast for a long way. Wouldn't that be expecting too much?
Wouldn't a small airframe be struggling to carry much weaponry internally? If you stack it up with external stores (weapons/fuel) won't it be slow and unstealthy?
Over a long service life wouldn't the loss rate of pilots and airframes be higher with a single engine? No? But aren't they saying that the engine will run at elevated temps compared to current engines? Might this not suggest lower reliability. Sounds reasonable.
Wouldn't a super hot tailpipe tend to suck in heatseakers as the pilot ran for home with a low fuel problem? No one is claiming this to be a fast aircraft. So....isn't it likely to get run down on the way out of an engagement? Some of those Sukhois get crackin', I believe.
I think so.
The airframe is small. Small airframes are associated with limited fuel capacity and thus range. A small airframe won't carry a lot of bulky, heavy weaponry plus heaps of internal fuel to fly fast for a long way. Wouldn't that be expecting too much?
Wouldn't a small airframe be struggling to carry much weaponry internally? If you stack it up with external stores (weapons/fuel) won't it be slow and unstealthy?
Over a long service life wouldn't the loss rate of pilots and airframes be higher with a single engine? No? But aren't they saying that the engine will run at elevated temps compared to current engines? Might this not suggest lower reliability. Sounds reasonable.
Wouldn't a super hot tailpipe tend to suck in heatseakers as the pilot ran for home with a low fuel problem? No one is claiming this to be a fast aircraft. So....isn't it likely to get run down on the way out of an engagement? Some of those Sukhois get crackin', I believe.
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R755
I tried and tried to resist responding, but when I realized you were actually being serious when you said 'expert commentary available at Air Power Australia' I couldn't help myself...
The airframe is not small. Its empty weight is 30-35 000lb depending on which model you're talking about. So it's comparable to or slightly heavier than an F-15E. I've never heard anyone call the Strike Eagle small.
It carries between 14 - 20 000lb of fuel internally. Compared to a Sea Harrier's 5000lb, or a legacy F-16's 7500lb, of internal fuel that's a pretty reasonable figure don't you think?
In a stealthy fit, it carries 2 x 2000lb JDAM (or 1000lb ones if you're in a -B), and 2xAIM-120 internally, which is more than an F-117 could. It's far more likely to be carrying 8 x Small Diameter Bombs in the future, which is more than any aircraft of comparable size out there can carry internally.
If you hang a bunch of external stores on it then you're correct, the top speed goes down and the radar cross-section goes up. But even the chimps at Air Power Australia understand that you wouldn't start hanging external stores on it until you'd achieved air dominance.
There have been a number of single-engined aircraft that have had quite successful service lives. Sopwith Camel, Fokker Eindecker, Spitfire, Mustang, Fw-190, F-86, Mig-15, F-100, F-8, Mig-21, A-7, F-16, Gripen, Rafale and many, many more. I'm not sure but I think Pratt & Witney have done a few careful sums to figure out how hot they can run their engine.
How did your war-gaming get to the point where all F-35s will start all of their engagements with Sukhois in a fuel critical state, with no weapons and trying to outrun them in a straight race? Did you consider the possibility that a stealthy F-35 might have side-stepped the Sukhoi before he even saw him, or (and this is a crazy notion) he may have positioned himself to take a face shot on the Sukhoi? Or, an equally crazy notion is that if he does think he's likely to get tangled up the F-35 pilot may have a wingman or 2 (possibly F-22s or Typhoons even) and will be calling for a de-louse long long before the Sukhoi gets in his shorts.
Regards,
Single Seat, Single Engine, The Only Way To Fly
I tried and tried to resist responding, but when I realized you were actually being serious when you said 'expert commentary available at Air Power Australia' I couldn't help myself...
The airframe is not small. Its empty weight is 30-35 000lb depending on which model you're talking about. So it's comparable to or slightly heavier than an F-15E. I've never heard anyone call the Strike Eagle small.
It carries between 14 - 20 000lb of fuel internally. Compared to a Sea Harrier's 5000lb, or a legacy F-16's 7500lb, of internal fuel that's a pretty reasonable figure don't you think?
In a stealthy fit, it carries 2 x 2000lb JDAM (or 1000lb ones if you're in a -B), and 2xAIM-120 internally, which is more than an F-117 could. It's far more likely to be carrying 8 x Small Diameter Bombs in the future, which is more than any aircraft of comparable size out there can carry internally.
If you hang a bunch of external stores on it then you're correct, the top speed goes down and the radar cross-section goes up. But even the chimps at Air Power Australia understand that you wouldn't start hanging external stores on it until you'd achieved air dominance.
There have been a number of single-engined aircraft that have had quite successful service lives. Sopwith Camel, Fokker Eindecker, Spitfire, Mustang, Fw-190, F-86, Mig-15, F-100, F-8, Mig-21, A-7, F-16, Gripen, Rafale and many, many more. I'm not sure but I think Pratt & Witney have done a few careful sums to figure out how hot they can run their engine.
How did your war-gaming get to the point where all F-35s will start all of their engagements with Sukhois in a fuel critical state, with no weapons and trying to outrun them in a straight race? Did you consider the possibility that a stealthy F-35 might have side-stepped the Sukhoi before he even saw him, or (and this is a crazy notion) he may have positioned himself to take a face shot on the Sukhoi? Or, an equally crazy notion is that if he does think he's likely to get tangled up the F-35 pilot may have a wingman or 2 (possibly F-22s or Typhoons even) and will be calling for a de-louse long long before the Sukhoi gets in his shorts.
Regards,
Single Seat, Single Engine, The Only Way To Fly